The present invention pertains generally to chemical lasers that use Iodine gas as an input stream. More particularly, the present invention pertains to systems for producing a gas having a high concentration of molecular Iodine for use in a chemical laser. The present invention is particularly, but not exclusively, useful as an on-demand, molecular Iodine gas supply system for an Iodine laser.
The Chemical-Oxygen-Iodine-Laser (COIL) is potentially useful for both military and commercial applications because it is capable of producing a high power laser beam. In the COIL process, Iodine gas is combined with singlet delta Oxygen in a laser cavity to produce a laser beam. In most COIL applications, it is preferable to use molecular Iodine at low temperatures, rather than atomic Iodine at high temperatures as an input stream to the laser cavity. In particular, low temperature molecular Iodine is much less corrosive than high temperature atomic Iodine. Iodine is a solid at room temperature. It must therefore be vaporized to produce the Iodine gas required in the COIL laser cavity.
One method for producing Iodine gas involves melting Iodine in an Iodine reservoir. The Iodine vapors that are given off by the molten Iodine are then transported using a carrier gas to the laser cavity through a delivery system. In general, the required delivery system involves piping and other complex parts such as valves, precision orifices, and temperature and pressure instruments. Unfortunately, this method of producing gaseous Iodine has several drawbacks. For instance, the entire delivery system, including the carrier gas, must be preheated and maintained at elevated temperatures to prevent Iodine condensation from plugging the delivery system. For a typical COIL system that is designed for military applications, several hours are required to melt the Iodine and preheat the delivery system. On the other hand, the source for generating the singlet delta Oxygen that is to be combined with the Iodine gas requires, only a fraction of a minute to reach operational status.
In the molten and gaseous states, Iodine is extremely corrosive. Because of Iodine""s corrosivity, equipment exposed to Iodine, such as the Iodine reservoir and delivery system described above, must be fabricated from expensive materials such as Hastelloy C-276. In addition to degrading any exposed equipment, the corrosion reaction will, with time at temperature, contaminate the Iodine in the reservoir, requiring the Iodine in the reservoir to be periodically purified or discarded. Impurities in the Iodine must be maintained at very low levels as they may be transported to the laser cavity where they can coat the optical components. For military applications, where readiness is important, a reservoir of molten Iodine would be required at all times, leading to a significant amount of corrosion. Furthermore, the delivery system valves, which must be operated hot and in the presence of Iodine will deteriorate with time at temperature and leak allowing corrosive Iodine to escape. Such a leak could be potentially harmful to electronic equipment. For these reasons, in order to perform routine maintenance on the molten Iodine reservoir and delivery system, these systems must be periodically shut down and allowed to cool. Additionally, maintenance of liquid Iodine systems creates a large amount of Iodine contaminated waste that requires special handling and disposal. In summary, the molten Iodine reservoir and delivery system is large, heavy, costly and complex.
The present invention recognizes that a gas containing Iodine can be generated by the combustion of a solid, fuel/oxidizer mixture that contains Iodine. The Iodine compound can be present in either the oxidizer, the fuel or both. By using a solid source of Iodine, the problems associated with the use of liquid Iodine are prevented and a supply of gaseous Iodine can be quickly produced. An example of a fuel/oxidizer system that can be combusted to produce gaseous Iodine is Cl4 fuel and Iodine Pentoxide (I2O5) oxidizer. Unfortunately, when a stoichiometric ratio of this fuel/oxidizer mixture is ignited, the resulting combustion reaction is very exothermic, producing a high temperature combustion gas that contains mostly atomic Iodine. In general, for Iodine containing gases at high temperatures, most of the Iodine is present as atomic Iodine, whereas at lower gas temperatures, most of the Iodine is present as molecular Iodine. As indicated above, for most COIL applications, it is preferable to use molecular Iodine gas as an input stream.
In light of the above, it is an object of the present invention to provide a system for generating a gas having a high concentration of molecular Iodine for use in a chemical laser. It is another object of the present invention to provide an on-demand, molecular Iodine gas supply system for a chemical laser that does not require a liquid Iodine reservoir to be maintained during periods of non-demand. It is still another object of the present invention to provide a gas, a chemical laser having a higher concentration of molecular Iodine than is obtained during combustion of a stoichiometric ratio of a solid, Iodine containing fuel and oxidizer system. Yet another object of the present invention is to provide an on-demand, molecular Iodine gas supply system which is easy to use, relatively simple to implement, and comparatively cost effective.
The present invention is directed to a method for generating a gas having a relatively high concentration of molecular Iodine for introduction into the laser cavity of an Iodine laser such as a Chemical-Oxygen-Iodine-Laser (COIL) or the All Gas Iodine Laser (AGIL). In the laser cavity, the molecular Iodine gas can be used to efficiently produce a high power laser beam. For example, in the COIL, the molecular Iodine gas can be combined with singlet delta Oxygen to produce a laser beam. For the present invention, the method includes the step of preparing a solid mixture that can be ignited to generate a gas having a high concentration of molecular Iodine.
In accordance with the present invention, the solid mixture contains a primary component and an additive component. The primary component of the mixture is composed of oxidizer and fuel at a substantially stoichiometric ratio. For the present invention, the primary component contains at least one Iodine compound. The Iodine compound can be present in either the oxidizer, the fuel or both. As such, the primary component of the mixture defines a combustion gas composition (i.e. the molecular Iodine concentration of the gas obtained if the primary component, alone, is ignited). Furthermore, this combustion gas composition has a specific molecular Iodine concentration. In this same manner, the primary component also defines a primary component combustion gas temperature (i.e. the temperature of the gas obtained if the primary component, alone, is ignited).
Examples of fuel/oxidizer systems that can be used in the present invention include; Cl4/Iodine Pentoxide (I2O5), Cl4/NH4NO3 and Polybutadiene/Iodine Pentoxide (I2O5). When these fuel/oxidizer systems are ignited, the resulting combustion reaction is very exothermic, producing a high temperature combustion gas. At this high temperature, most of the Iodine is present as atomic Iodine. For the present invention, the mixture includes an additive that causes the mixture to produce a lower temperature combustion gas than would be produced by the primary component when combusted alone. In the lower temperature combustion gas, most of the Iodine is present as molecular Iodine rather than atomic Iodine. As indicated above, molecular Iodine is favored by the COIL system. Thus, the solid mixture with the additive component produces a combustion gas having a higher molecular Iodine concentration than is obtained by combustion of the primary component alone. Stated another way, the gas resulting from ignition of the mixture (with the additive component) has a higher molecular Iodine concentration and lower temperature than the gas resulting from the ignition of the stoichiometric ratio of the fuel and oxidizer used to prepare the primary component of the mixture.
In one preferred embodiment of the present invention, the additive component is an Iodine compound that absorbs heat during decomposition. For example, Iodine Pentoxide (I2O5), which absorbs heat during decomposition into Iodine and Oxygen, can be used as the additive component. It is to be appreciated that when Iodine Pentoxide (I2O5) is used as the additive, a lean, non-stoichiometric mixture results. One advantage of using Iodine Pentoxide (I2O5) as the additive is that additional molecular Iodine is added to the combustion gas by the decomposition of the Iodine Pentoxide (I2O5). In another preferred embodiment of the present invention, the additive component is an Iodine compound that absorbs heat during sublimation. One example of an Iodine compound that absorbs heat during sublimation is solid Iodine. The use of solid Iodine as the additive also increases the molecular Iodine in the combustion gas due to the molecular Iodine that results from the sublimation of the solid Iodine.